Marathoner,
A couple of comments from a guy whose wife divorced him 5 years ago (over very different views of money and the fact that she was dating someone else):
1. You will be OK in time, and you'll probably be great in time. But it can take longer than others expect. I've heard a rule of thumb that it's 1 year of recovery for every 2-3 years of marriage. I was married for 15 years and it took me 5 years to get to a point where I am finally good. So even though some people will say you should be fine in 6 months to a year, please give yourself years if you need it. Also, you'll alternatively make steady progress and periodically have times of sadness/frustration/loneliness/anger/grief/etc, but you will make progress over time if you have faith in yourself and don't lose hope.
2. Divorce laws vary by state, as you probably already have heard. That having been said, I believe most states are now no-fault, meaning the court could care less who has been nice and who is the real jerk; they just split assets/debt roughly down the middle, give or take some depending on the circumstances. Read the law in your state, find an attorney you feel comfortable working with, and ask him or her what is reasonable or likely.
3. I highly recommend attorney-based mediation; it is faster, cheaper, and more under your control than going to court. You have your attorney, he has his attorney, and you go to a third one and hash out an agreement between the two of you. Once you have something that you both can live with, you each check with your own attorneys to make sure you haven't been taken advantage of. It's not binding unless you both agree, then a judge just stamps the thing and makes it official. The advantage of an attorney-mediator is that they can write it all up for you both, and can also probably give you both a pretty good idea of what the courts would end up doing anyway. The relevant phrase here is "stipulated divorce".
4. He has probably cheated on you before, this is probably just the first time you've caught him. As you get enough road time on being by yourself, you'll maybe even be able to look back and see clues. Cheaters almost never come clean and stay clean for the rest of their lives either, so even if he really wants to change you can probably plan on him falling off the wagon again in the future. I'd suggest asking yourself if that's what you really want.
5. This comment will probably draw controversy, but I would make sure you're OK on your own for a while and not start into a relationship too soon. It is tempting (and many others may recommend) to be in a relationship just because it is what you've been used to, and relationships do have their benefits. But it can also prevent you from really taking stock of yourself and your life, and deciding where you want to go in this world, who you want to become, what you want your life to look like. If you shortchange that analysis and work, you may find yourself ending up with someone who isn't right for you for the long run. [Full disclosure: I haven't been on a date since my ex and I separated, and I'm glad because I know that I'm a much healthier person now.]
6. Make all of your decisions from this point forward on what is best for you. This is not selfish; this is being levelheaded in a situation where your marriage is probably over and you could easily regret being overly nice to him in the negotiations out of a misplaced guilt or manipulation by him. Treat it like a business deal. For example, he says he's in no hurry. Fine, but if you decide it would be better for you to have the divorce go faster, talk with your attorney and take steps to make things go faster.
Finally, the vengeance card is overrated in my view. I made the decision early on to treat my ex civilly and reasonably throughout the whole deal, even when I thought she was being unreasonable. (I tried to remember that she probably thought me unreasonable at times.) In turn, she treated me pretty decently through the process too. Anyway, I have regrets about things I did and didn't do and about things I said (starting with "Will you marry me?"
) and didn't say during the marriage, but I can say that I was a decent guy during my divorce and I sleep better at night and stand a little taller having done that. My motivation was partly because of our kids, but even in the no-kids case there is a measure of self-respect that a person can be proud of later.
Good luck, and remember that life does get better over time.
2Cor521